For more than a century, fossil fuels have been the primary feedstock for the chemical industries. However, new discoveries of fossil fuel deposits are diminishing whilst demand for fossil fuel based chemicals are ever increasing, and soon the supply of fossil fuels will be outweighed by the demand. In an attempt to address this issue a large amount of effort has gone into developing novel biotechnological strategies for producing chemical feedstock from renewable sources (e.g. sugars). In 2004 the Department of Energy in the USA identified a list of 12 target feedstock chemicals to be produced through biotechnological routes. 3-hydroxy propionic acid (3-HP) has been chosen as one of the 12 feedstock chemicals as it can serve as a platform for the development of a range of 3-carbon petrochemical intermediates, and in particular it can be dehydrated to form acrylic acid. More than 1 billion kilograms of acrylic acid are produced annually as it is the monomeric building block for polymeric acrylates which can be used in a wide range of consumer products, e.g. personal care products, adhesives, coatings and paints, and the annual total market size is over USD100 billion. One particularly important application of 3-HP is for the production of superabsorbent polymers (SAP), which constitute a significant part of baby diapers and incontinence products. It is evidently desirable to develop a more sustainable way of producing acrylic acid, hence this is why a significant amount of research continues towards the development of a biotechnological method of producing 3-HP, the acrylic acid precursor.
Conventional biological processes for producing 3-HP are performed by a complicated metabolic pathway. Therefore, it is difficult to control the process effectively, resulting in low production yield and productivity. For this reason it is necessary to design a 3-HP production pathway which controls the quantity of biochemical precursors in the cytosol such that the flux towards late stage biochemical intermediates in said 3-HP production pathway is favoured and alternative biological pathways are disfavoured.
EP 2505656 discloses a method of producing 3-HP using a malonic semialdehyde reducing pathway, wherein the process utilises an NADPH dependent malonyl-CoA reductase which may be derived from C. aurantiacus and an NADP/NADPH dependent GAPDH variant to resolve a redox imbalance within the metabolic process. The maximum reported yield of 3-HP was approximately 1.3 g/L.
Rathnasingh et al. (J. Biotechnol. 2012) discloses a method of producing 3-HP using Escherichia coli cells, wherein said cells overexpress MCR from C. aurantiacus and ACC in the malonyl-CoA pathway. The maximum reported yield of 3-HP was 2.14 mmol/L (0.19 g/L).
WO 2008/080124 discloses a method of producing butanol using modified yeast, wherein said method produces increased quantities of cytosolic acetyl-CoA by overexpressing PDC1 and ALD6 which may be derived from S. cerevisiae and ACS which may be derived from S. entherica. This method does not utilise the malonyl-CoA pathway.
WO 2007/024718 discloses a method of producing isoprenoid compounds using genetically modified host cells, wherein said cells are modified to produce increased levels of acetyl-CoA by increasing ALD and ACS activity. This method does not utilise the malonyl-CoA pathway.
In S. cerevisiae, acetyl-CoA carboxylase is tightly regulated at the transcriptional, translational and post-translational levels (Shirra, M. K. et al, 2001; Nielsen, J. 2009). At the level of the protein, Snf1 kinase is the major kinase which phosphorylates and inactivates ACC1 in vivo (Shirra, M. K. et al, 2001). WO 2012/017083 discloses a method of producing wax esters using modified yeast, wherein the quantity of cytosolic acetyl-CoA is increased through increasing the activity of ACC1 by mutating ACC1 at dephosphorylation sites such that it is no longer inactivated by Snf1.